4 years ago

Reliability of Constant Charge Method for Molecular Dynamics Simulations on EDLCs in Nanometer and Sub-Nanometer Spaces

Reliability of Constant Charge Method for Molecular Dynamics Simulations on EDLCs in Nanometer and Sub-Nanometer Spaces
Kefa Cen, Zheng Bo, Hualei Qi, Jing Kong, Huachao Yang, Jianhua Yan, Jinyuan Yang
The constant charge method (CCM) and constant potential method (CPM) are two major techniques to apply electric charges on electrodes for molecular dynamics (MD) simulations on electric double-layer capacitors (EDLCs). Compared with CCM, CPM is more realistic since the influence of electrode polarization is taken into account, although computationally more expensive. In this work, the reliability of CCM for MD simulations on EDLCs in nanometer and sub-nanometer spaces is investigated. Particular attention is paid to the comparison of CCM and CPM for modeling EDLCs in terms of ion concentration and EDL structures in such nano/sub-nano confined spaces, which are widely found in graphene-based materials. The deviation for ion concentration calculated from CCM and CPM was found to be significant in both neutral and charged confined spaces (e. g., deviation ratio of 40.27 % and 11.18 % for Cl− ions in neutral and charged 9 Å space, respectively), which is different from previous observations in bulk solutions. This result could be attributed to the strong electrode polarization in nano/sub-nano confined spaces. Although CCM and CPM yielded essentially similar EDL structures, the time evolution of electrode charge with a potential difference could be conducted only with CPM. The findings of the current work could provide useful insights for choosing appropriate methods for MD simulation on EDLCs in nano/sub-nano confined spaces. A comparison of simulation methods: The reliability of the constant-charge-method-based constant potential method for MD simulations on electric double-layer capacitors in nanometer and sub-nanometer spaces is investigated. A significant deviation of the constant charge method for the ion concentration and dynamics of the electric double-layer formation in these confined spaces is found.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/celc.201700447

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